1. Field of the Invention
The present invention relates to a fuse structure, and more particularly, to a fuse structure having at least one fuse including a thin portion and a thick portion formed from a single-layered material.
2. Description of the Prior Art
Aluminum alloys with silicon dioxide (SiO2) dielectrics have been the materials of choice for interconnect systems since the dawn of the integrated circuit (IC) era. These materials were convenient to process using mature subtractive etch processes for metal line patterning. However, as ICs have relentlessly marched down the path towards smaller geometry and to a deep sub-micron generation in the pursuit of increased speed, the traditional Al/SiO2 interconnect system has shown itself to be a limiting factor. Cu-dual damascene architectures with low-k dielectrics are thus developing and becoming the norm now in forming interconnects. Overall, RC delays occurring during signal transmission are reduced and operating performance is improved because Cu has a 40% less resistivity compared with aluminum, and low-k materials reduce the capacitance between interconnections.
In an integrated circuit, each transistor or cell needs to be electrically connected to corresponding metal lines within different metal layers after being formed. Then the transistors are electrically connected to bonding pads through each metal line. After being packaged, the integrated circuit is electrically connected to an external circuit through terminals, which are electrically connected to bonding pads. In a memory device, structures known as fuses are usually formed within the top metal layer. If there are portions of malfunctioning memory cells, word lines, or metal lines in a completed memory device, some redundant cells, redundant word lines, or redundant metal lines are utilized to replace them. The method is to use a laser zip step to sever fuses. Then a laser repair step including laser cutting, laser linking, etc., is used to sever the original electrical connection to the malfunctioning memory cells, word lines, or metal lines, or to form some new electrical connection to compensate the useless memory cells, word lines, or metal lines.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a fuse structure 10 on a semiconductor wafer according to the prior art. As shown in FIG. 1, the prior art fuse structure 10 comprises at least one memory cell (not shown) or at least one transistor (not shown) disposed on a silicon substrate 11 on a semiconductor wafer 12 and individual metal lines 14. Different metal lines 12 are isolated by a first dielectric layer 16.
The metal line 14 comprises an aluminum line or a copper line. In the case where the aluminum lines are used, a continuous process including deposition, photolithography, and etching is utilized. In the case where the copper lines are used, a dual damascence process is usually utilized. The reason is that the aluminum lines are usually formed by a DC magnetron sputtering process, which is characterized by its poor step coverage ability. In the process generation beyond 0.13 μm, line width is smaller, aspect ratio is relatively increased, and the poor step coverage ability causes a severe problem. Although a high temperature (>400° C.) aluminum process with an improved step coverage ability due to a high surface migration rate at high temperature has been developed, it is not satisfactory. However, aluminum is easily deposited and etched, and is very cheap as well. Thus, the aluminum line is widely utilized in semiconductor factories. Although the cooper lines are superior to the aluminum lines in terms of electrical performance, the etching process for the copper lines cannot be done in a chemical way because of the poor volatile ability of copper-chloride-alloy, which is a drawback of the copper lines. The copper is etched by physical momentum produced by the bombardment of ions in plasma on the copper, hence the copper lines is formed by the dual damascence process to skip the etching process for copper.
The fuse structure 10 further comprises a second dielectric layer 18 disposed on the first dielectric layer 16 and the metal lines 14, at least one conductive plug 22 disposed in the second dielectric layer 18, and at least one bonding pad 24 and at least one fuse 26 disposed on the second dielectric layer 18. Similar to the metal lines 14, the composition material for both the bonding pad 24 and the fuse 26 comprises aluminum or copper. Therefore, the conductive plug 22 may be formed by forming a via hole 28 extending from the top surface of the metal lines 14 up to the top surface of the second dielectric layer 18 first, followed by filling metal material into the via hole 28. After that, the bonding pad 24 and the fuse 26 are formed on top of the corresponding conductive plug 22 by utilizing a continuous deposition, photolithography, and anisotropic dry etching process. Or, the bonding pad 24, the fuse 26, and the conductive plugs 22 are simultaneously formed in a dual damascene process.
As shown in FIG. 1, the fuse structure 10 further comprises a third dielectric layer 32 and an opening 34 in the third dielectric layer 32. The third dielectric layer 32 is disposed on the second dielectric layer 18, the bonding pad 24, and the fuse 26. The opening 34 exposes portions of the bonding pad 24. The metal material of the bonding pad 24 is thus exposed so the testing and packaging processes can be performed. The third dielectric layer 32 is also called as a passivation layer. In addition, the third dielectric layer 32 is a transparent material layer. Actually, an etching back process is performed from the top surface of a third dielectric thin film (not shown) downwards to form the thin third dielectric layer 32 so the laser beam is able to transmit and sever the fuse 26 in the subsequent laser zip process.
Since the composition material for both the bonding pad 24 and the fuse 26 comprise aluminum or copper, the fuse 26 is an aluminum fuse or a copper fuse. When the fuse 26 is a copper fuse, the fuse 26 is usually formed by performing an electroplating process in a dual damascene process, which is previously mentioned. However, copper is difficult to evaporate during the laser zip process because of its high melting point. A splash phenomenon results and causes difficulty in assuring high reliability. If the fuse 26 is an aluminum fuse, its thickness is increased in the process generation beyond 0.13 μm to prevent the occurrence of an open circuit due to the electromigration tendency of aluminum. To increase the thickness of the fuse 26 brings difficulty to the process, and it is difficult to sever the fuse 26. Although the energy of laser beam can be adjusted by adjusting the laser spot size, however, the higher the energy of laser beam, the higher probability of damaging the structure underneath. If the conductive plug 22 is an aluminum conductive plug, its poor step coverage ability easily induces problems.
It is therefore very important to develop a new fuse structure. This fuse structure should not bring difficulty to the subsequent laser zip process no matter what composition materials for both the bonding pad and the fuse are.